It is frequently desirable to analyze the breath of a human individual to determine whether the breath contains a particular chemical compound, such as ethyl alcohol or carbon dioxide, or a non chemical, such as a particular microorganism. Prior-art workers have provided numerous methods and devices for obtaining samples of breath for such analysis. It was recognized early in this art that obtaining samples of breath to be analyzed presents three main problems. One of the more important and difficult of these problems is to ensure that the sample of breath obtained is at least primarily alveolar gas, i.e., gas contained in the alveoli rather than from the mouth, throat and bronchials. In exhalation, as the lungs contract, breath contained in the mouth, throat and bronchials is necessarily exhaled first, followed by the breath contained in the alveoli of the lungs. Since it is at the alveoli where the exchange of substances between breath and blood ultimately occurs, the concentration of gaseous or vaporous constituents in the alveoli corresponds more closely to the concentration of substances dissolved in the blood. Thus, if a sample of breath is to be analyzed for the presence of constituents which may be present in the blood, the sample of breath analyzed must be at least primarily alveolar gas. Similarly, an alveolar sample is required for best detection of, e.g., microorganisms in the lungs. A usual approach to this problem has been to direct the early portion of exhalation into a first chamber, then to direct the last portion of exhaled gas into a second chamber, the gas collected in the second chamber being the sample for testing or analysis. Methods and devices typical of this approach are disclosed in U.S. Pat. Nos. 2,795,223, Stampe; 3,544,273, McConnaughey; 3,676,073, Luckey; and 3,734,692, Lucker et al. Other prior art workers have adopted the approach of employing only a single chamber, into which all of the breath is exhaled, and providing flow means such that at least some of the breath escapes from the chamber, only the later portion of the exhaled breath being intended to remain in the chamber for testing. Typical methods and devices of this type are disclosed in U.S. Pat. Nos. 1,685,557, Legelsberger, 3,303,840, Etslinger and 3,858,573, Ryan et al. Another problem encountered is that of obtaining a sample of substantially predetermined volume and then presenting the collected sample for testing or analysis. In efforts to solve this problem, it is frequently proposed to employ an elastically expansible container, typically a balloon, to collect the sample, with the elasticity of the balloon acting to expel the collected sample for testing or analysis as the balloon deflates. In other efforts to solve this problem, it has been proposed to employ an inelastic container of such nature that the container can be collapsed by hand pressure to expel the collected sample for testing or analysis, as in the Etslinger and Lucker et al patents, or of such nature that the sample is pumped from the container, as in the Ryan et al patent. In addition to these problems, the trade has imposed the requirement that the device employd to collect and present the breath sample must be simple, inexpensive and difficult for the user to defeat. Though some prior-art devices and methods have achieved commercial acceptance, all suffer from failure to satisfactorily solve at least one of the problems just mentioned and there has been a continuing need for improvement.